A light string that includes plural light sources directly soldered onto electric conductors at intervals, so as to form a string-shaped illumination device without a lamp holder, is known in the art. An example of such a light string is found in U.S. Pat. No. 8,397,381, entitled Method of Manufacturing Light Set with Surface Mounted Light Emitting Components. Light strings having many small-sized light sources, such as small bulbs that include light emitting diodes (LEDs), are commonly known. A light string is as flexible as the electric wire is, such that the light string is easily arranged in any configuration to comply with requirements for special illumination or decoration.
In the art, light sources are soldered to the copper core or conductor after the insulating layer of the electric wire or wire is removed, and then an electrical insulating treatment is performed on the solder joints. In this approach, light sources obviously stick out on the electric wire and are configured to have high-directivity. When arranging a light string, which may include pulling the light string, the light sources may be subject to forces and shocks that result in solder joints cracking. Furthermore, usually electric wires are flexible, but the soldering material is not as flexible. Thus, when the electric wire of the light string is pulled or bent, stress concentration often occurs at the soldering joints and results in soldering joints cracking.
In addition, in a light string, light sources are typically electrically connected in series or electrically connected in parallel. In parallel, precise driving voltage is required to drive the light source and prevent the light sources from being damaged by over-current. In a series connection, the number of the light sources is determined by the output voltage of the power source, with the number and type of light source being selected to ensure that every light source is driven by an appropriate voltage with an allowable voltage difference. This means that the number of the light sources is restricted by the output of the power source such that the number cannot be changed at will. Meanwhile, one damaged light can result in failure of the whole light string.